Immunogenicity and safety of AZD1222 (ChAdOx1 nCoV-19) against SARS-CoV-2 in Japan: A double-blind, randomized controlled phase 1/2 trial.

Abstract Background Immunogenicity and safety of the AZD1222 (ChAdOx1 nCoV-19) vaccine was evaluated in Japanese adults in an ongoing phase 1/2, randomized, double-blind, parallel-group, placebo-controlled, multicenter trial (NCT04568031). Methods Adults (N=256; age ≥18 years) seronegative for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were stratified by age into 18–55- (n=128), 56–69- (n=86), and ≥70-year-old cohorts (n=42), then randomized 3:1 to receive AZD1222 or placebo (2 intramuscular injections 4 weeks apart). Immunogenicity and safety were coprimary endpoints. Data collected up to Day 57 are reported. Results Positive seroresponses to SARS-CoV-2 spike and receptor-binding domain antigens were seen in all 174 participants who received 2 doses of AZD1222. Neutralizing antibody seroresponses were seen in 67.5%, 60.3%, and 50.0% of participants receiving AZD1222 aged 18–55, 56–69, and ≥70 years, respectively. Solicited adverse events (AEs) were typically mild/moderate in severity and included injection site pain and tenderness, malaise, fatigue, muscle pains, and headache. Common unsolicited AEs included injection site pain and tenderness, fatigue, and elevated body temperature. No vaccine-related serious AEs or deaths were reported. Conclusions AZD1222 elicited a strong humoral immune response against SARS-CoV-2 and was well tolerated in Japanese participants, including elderly participants.